The present invention relates to all-aromatic polyester resin compositions.
All-aromatic polyester resins have excellent heat resistance as well as good resistance to chemical, oil and radiation and good insulating properties and are injection moldable. So their use is increasing in wider fields, especially for electric or electronic components. But, the moldings of all-aromatic polyester resin tend to warp or crack because of high temperature for injection molding, its flow characteristics susceptible to the molding temperature, and its high tendency to orientation. Also the moldings have been thought to be not suitable for practical applications to structural materials because of their poor impact strength.
A number of attempts have been made to obviate such shortcomings of all-aromatic polyester resins. In order to improve its flow characteristics, blending such resins as polyethylene terephthalate or polycarbonate having good flow characteristics (or moldability), and melting and blending such resins as polyphenylene sulfide or polyether ether ketone having high heat resistance as well as good flow characteristics have been proposed. In order to improve the impact resistance of the moldings, blending rubber is one solution. However, in mixing an all-aromatic polyester resin with polyethylene terephthalate or polycarbonate, granulating and molding, if treated at a temperature which melts the all-aromatic polyester resin into a uniform structure, polyethylene terephthalate and polycarbonate are apt to heat-decompose. On the other hand, if treated at a temperature at which the resin does not heat-decompose, the flow characteristics of all-aromatic polyester resin will not be improved so sufficiently that the composition will be a uniform dispersion. Similar unfavorable results are observed in blending rubber to improve the impact strength. It was further noted that an expected decrease in the melt viscosity of an all-aromatic polyester resin was not attained by melting and blending polyphenylene sulfide or polyether ether ketone with the all-aromatic polyester resin. Besides the above methods, it is thought that introducing an aliphatic group such as ethylene glycol as a soft segment into the molecular structure to modify the properties of the all-aromatic polyester resin itself to lessen its cohesiveness would improve the flow characteristics and decrease the anisotropy. But this method is in no way favorable because it deteriorates drastically the heat resistance of the all-aromatic polyester resin.